I have no idea where to start this problem. I know that I need to figure out whether the diodes are on or not, and then replace them with the appropriate resistance, but I'm not sure how to go about doing that. Any help is appreciated. Thank you.

 

The diode model you are using does not have a resistance. If the diode is OFF then it looks like an open circuit (infinite resistance if you like), but if the diode is ON then it looks like a 0.7 V battery with zero resistance.

 

Vx is approx 10.7V,